Image formations and various methods to form coated film, including a patterned coated film on the supporting body, using the inkjet methods, are well known. An inkjet head, being used in the inkjet methods, incorporates a plurality of nozzles to jet ink onto the supporting body, and forms a desired image or the coated film onto the supporting body, based on printing data.
The above described inkjet operation is to jet minute ink droplets from the nozzles onto the supporting body by a piezoelectric element, a heater, or the like. For example, the piezoelectric element is mounted on the nozzle, whereby the piezoelectric element is controlled to change its shape, due to an applied electrical driving voltage. That is, since the shape of the piezoelectric element is changed by the applied electrical driving voltage, an ink channel is compressed so that the ink droplet is discharged from the nozzle.
In the present Specification, said “ink” is equal to “coating solution”, and “to print” is equal to “to coat” in their meanings.
As the methods to form the above described image and coated film on the supporting body exhibiting the wide range, well known are a serial type method which conducts the coating operation while the inkjet heads are controlled to move in a conveyance direction or a width direction of the supporting body, and a line-type method which conducts the coating operation while the plurality of the inkjet heads are configured to be mounted in the width direction of the supporting body. Specifically, concerning said line-type method, the plurality of the inkjet heads are provided to cover the intended coating width of the supporting body, in parallel to the width direction of the supporting body.
To form the coated film on the long-roll supporting body, which is continuously conveyed, the above described line-type method does not need to scan the supporting body in a so-called sub-scanning direction of the inkjet heads, whereby the accuracy of landing positions of the coating solution can be improved. Further, the coating speed can be increased.
Various products, which are produced after the coated film have been formed on the continuously conveyed long-roll supporting body, are not limited to specific members, so that the above various products include, silver halide photosensitive members for general use and the industrial uses, heat sensitive members, heat development photosensitive members, and devices for electro-optical panels including photo-resist, LCD and organic EL. Concerning the devices for the electro-optical panels, listed is an optical film, on which an antireflective layer is formed, to be attached on the front surface of a display device, in order to more clearly view images through a CRT or a liquid crystal display device. However, concerning the large screen display devices, such as a television device, said screen tends to be easily scratched by something undesired. To overcome this problem, a hard-coat layer is formed on the supporting body, and the antireflective layer is formed on said hard-coat layer, whereby an antireflective film, including the hard-coat layer on the antireflective layer, is produced. Said optical film is requested to exhibit a very accurate thickness of the coated film, because any distortion of the transmitted light or any distortion of the reflected light must be extremely even, as well as that the amount of transmitted light must be extremely even. Specifically, in the case of the antireflective film, due to the optical interference of beams of light, reflected on an upper surface of the coated film, and beams of light, reflected on a lower surface of the coated film, the incident light is attenuated so that the amount of reflected light is reduced, whereby the power of antireflection depends upon the thickness of the coated layer while the thickness of the coated layer is based on the wave length of the incident light. That is, higher evenness of the coated film results in higher quality of the antireflective layer.
However, in a case of the jetting operation of ink droplets as the inkjet method, conditions while letting the ink droplets tend to vary, which conditions depend upon the pressure at a time just before the ink enters the inkjet heads. That is, said conditions depend upon the back-pressure on the ink. If the back-pressure is abnormally high, the volume of ink droplets to be jetted increases, whereby a satellite area of each deposited ink droplet increases, and the nozzle plate supporting the nozzles tends to be quickly stained. Further, an extraordinarily high back-pressure causes abnormal leakage of ink droplets during non-jetting condition, which also stains the nozzle plate, as well as abnormal dripping of ink droplets. On the other hand, if the back-pressure is relatively low, the jetted volume of ink droplets decreases, and the ink jetting operation becomes unstable, and if the back-pressure is extraordinarily low, the ink jetting operation tends to become difficult, though the piezoelectric element may be working well.
Still further, the back-pressure is configured to be equal to or slightly less than the atmospheric pressure. Due to this configuration, the above described satellite area and dripping of ink droplets during the non-jetting condition are prevented, so that staining of the nozzle plate and dripping of ink droplets can be decreased. Due to these positive results, coating defects, such as a continuing streak or the like, can be prevented.
Specifically, concerning the above described line-type coating device, the coating operation tends to be continued for a long duration. During such duration, the inkjet heads can not be cleaned easily, so that any defective back-pressure results in a continuing streak. Accordingly, an adequate amount of pressure should be applied to the coating solution in the inkjet heads, so that the ink droplets can be stably jetted.
Concerning the back-pressure, a coating device is disclosed (see Patent Document 1), in which the level of solution, stored in a solution tank (which is a solution feeding tank), is maintained to be at a predetermined level, which is lower than the level of the nozzle surfaces of the inkjet heads, whereby the predetermined level, that is, the level of the nozzle surfaces and the level of the head of solution stored in the solution tank are controlled by level sensors to be constant (See Patent Document 1).
Patent Document 1: Unexamined Japanese Patent Application Publication No. 2004-223356.